Page 161 - Power Quality in Electrical Systems

Uninterruptible Power Supplies 143

choice. PEMFC fuel cells also have the highest power density of all of
the types in Table 9.1 [9.22]. Fuel cells utilizing hydrogen as fuel can
operate for relatively long periods of time—for example, hours—or for
short periods, in standby service, in the nature of engine-generator sets
or batteries.

Applications. Specific applications include the following:
■ Space (used on Gemini, Apollo, and space shuttle missions)
■ As a UPS, which requires instant availability of power when utility
service fails. The fuel cell by itself requires heating to start up. UTC
Fuel Cells show a 5-kW UPS to supply 48 V dc for telecom applica-
tions, which uses ultracapacitors to supply the energy during the
start up of the fuel cell system.
■ The telecom industry is considering fuel cells as an alternative to VRLA
batteries for sites requiring 1 to 3 kW for up to eight hours [9.20–22].
■ Nakamoto, et al. show a 4.5-kW fuel cell system to produce 300 V ac
power, Figures 9-13 and 9-14 [9.23].
■ Utility industry applications include a study by Sedghisigarchi and
Feliachi of 1.5-MW fuel cell systems and gas-turbine generators oper-
ating on a common bus in a 9-MW system [9.24].

Fuel line Power line Control line Water control line

Hydrogen Generation unit
cylinder Operation
box. Control unit Battery
panel
Hydrogen
sensor
Charger
H 2
Fuel cell
AC
100 V
Fuel electrode Inverter
Electrolyte Exhaust fan
Air Exhaust
H 2 H 2 Air electrode gas
Fan Water Water
vessel
Hydrogen cylinder
Figure 9.13 Block diagram of 4.5-kW fuel cell UPS [9.23].
[© 2000, IEEE, reprinted with permission]